Field of the Invention
The present invention relates to an element having a microstrip structure including an active layer, and an oscillator and an information acquiring device including the element.
Description of the Related Art
An electromagnetic wave in a terahertz frequency band approximately from 0.1 THz to 10 THz (hereinafter also referred to as a terahertz wave) can be applied to many fields. For example, many molecules and molecular complexes exhibit resonance in this frequency band. Therefore, spectrum analysis using a terahertz wave can be used for, for example, identification of various kinds of gases or substances that are not transparent to an electromagnetic wave at a frequency in a light region but are transparent to a terahertz wave. Therefore, terahertz imaging can be used for security check, quality control in a manufacturing process, and the like. Further, a terahertz wave can also be used for ultra-high speed wireless communication or the like.
For applications described above, a terahertz light source that is compact, is efficient, and operates at room temperature is desired. In recent years, a terahertz wave oscillator using an element including a resonant tunnel diode (RTD) receives attention as a promising candidate for a terahertz light source. Today, an RTD can emit a terahertz wave of up to approximately 1.8 THz. The RTD is very compact and sufficiently efficient, and thus, suitable for practical applications. Further, the RTD operates at room temperature. Those characteristics make practical applications of the RTD very attractive. However, an output power of the RTD is relatively small, which is not sufficient for many of the applications at present. This is a main weak point of the RTD.
In regards to the problem described above, in US Patent Application Publication No. 2015/0303559, the following technology is disclosed. Disclosed are some methods of emitting a terahertz wave from a microstrip waveguide connected to an antenna. Further, parameters of a waveguide with an RTD that is designed to oscillate an electromagnetic wave at approximately 0.2 THz are also disclosed.
In US Patent Application Publication No. 2007/0280319, the following technology of an active waveguide is disclosed. Disclosed is a configuration in which a passive metal-dielectric-metal waveguide is formed on a side portion of a core of the waveguide with an RTD.
In an element using the RTD, dimensions of the RTD are required to be small for the purpose of reducing the capacitance. If not, an operating frequency of the oscillator is limited. Meanwhile, in the terahertz band, the dimensions of the RTD are normally in the submicron range. When the dimensions are so small, the output power of the RTD is limited. Therefore, in order to attain higher output power in a frequency band up to the vicinity of 2 THz, it is necessary to optimize the configuration of the element including the RTD, to thereby attain both reduction in capacitance through miniaturization and securement of an electromagnetic wave gain.